With respect to research on type 1 diabetes (T1D), a major gap in the field has been the lack of reagents for the induction of antigen-specific tolerance. Identification of the beta-cell autoantigens that drive the pathogenic T cells in this disease has been a top priority for researchers since knowledge of these proteins could add considerably to our understanding of how diabetes develops, including the relative importance of antigens arising at different stages of disease. To identify antigens for a long- established panel of highly diabetogenic, NOD-derived T cell clones, we have used biochemical separation procedures and proteomic analysis to isolate proteins from islet beta-cells. This work has led to the recent discovery of a new autoantigen in T1D, the secretory granule protein, chromogranin A. The underlying hypothesis of this project is that the antigenic ligands for this panel of diabetogenic clones are derived from a set of closely related proteins and are generated through a common mechanism. To test this hypothesis, we have designed a project in which our goals are to identify antigens for diabetogenic T cells, define the mechanisms by which they arise, and characterize their biological relevance to disease. Our aims are to: (1) isolate the 2-cell antigens for islet- reactive, diabetogenic CD4 T cell clones, (2) determine the primary structure, including modifications, of antigenic peptides, and (3) determine whether WE14, a peptide from ChgA, can be used as a tolerogen to prevent or delay T1D. Expanding our knowledge of the proteins that are the sources of T cell peptide antigens will allow us to better understand their significance in T1D, and will provide the basis for specific therapeutic intervention at the level of the T cell. These proteins, and the peptide ligands from them, will provide information about autoimmune mechanisms, can be used for induction of antigen-specific tolerance or serve as targets for drug intervention, and may also assist in developing methods for early diagnosis and monitoring disease progression.